Many electronic devices are subject to various rules or regulations regarding their operation and use. For example, new equipment designed to operate on military platforms often needs to comply with long-established specifications for controlling the ripple current that the equipment can draw from military power supplies. As a particular example, the MIL-STD-461 document issued by the U.S. Department of Defense defines the CE101 requirement for power leads operating in the 30 Hz to 10 kHz range on military aircraft and submarines.
Wireless radios under development today are intended to support more complex radio frequency (RF) waveforms than previous radios. In older radios, a suitable RF envelope was often achieved using frequency modulation (FM), which provides a continuous RF output and causes a radio's input current to be continuous and virtually ripple-free. The use of amplitude modulation (AM) often needed some filtering to achieve suitable ripple values. The filtering was relatively simple unless the modulation included frequency components below 100 Hz, so limiting the low-end bandwidth of a signal corrected the problem. However, with newer modulation techniques (such as Have Quick, SINCGARS, WNW, LINK16, and MUOS), RF envelope waveforms are typically varied but repetitive. Using conventional power conversion circuits, a radio's input current would have the same form as its RF power output, so the radio's input power leads would fail the CE101 requirement.
A conventional solution for limiting ripple current is to install an LC filter between a power supply and a wireless radio. However, at low frequencies, an inductor in the LC filter typically needs to be extremely large. A rule of thumb is that the filter needs to be at least twice as large and twice as heavy as the transmitter it is filtering. This negatively impacts the size, weight, and cost of the wireless radio.